iHP-120 only works holding player upside-down

[michael]

Hello guys!

Day-to-day my 6-year old ihp-120 does´nt work holding it in a normal position. First I´d thought it is dead or has got a software problem because it won´t turn on lying as usual on its back in my hand or on the tabel.
Once I´ve tried it in a upside-down horizontal position (display shows to bottom) the player boots and works fine, but only in a range around some 180 degrees. Even when I only try to turn it from horizontal position into vertical,  the player stops playing, reacting on the buttons or even shutting down and the display freezes when it is nearly righted. When I move it back to horizontal, the player resumes what it is working on and vice versa. And, depending on how slowly it is turned to the breaking-point, an actually played audio sounds like a turntable abruptly loosing speed with a lots of crackle in the end.

I´m using Rockbox 3.8.1 but this also happens with the original firmware. I´ve tried a lot to manage it, tried it with the power supply, disassembled the whole player, changed the harddisk, tried it all with naked player, tried it without harddisk, searched for bad contacts, cleaned the circuit board but nothing worked to resolve or locate the problem. I did´nt changed the battery but I guess thats not the point.
Please excuse my bad english, I hope I could describe the problem even so comprehensible. I wonder if the player has got some positioning sensors but there seems to be definitly a cause on the players hardware related to its physical attitude. I would be glad about any suggestion, what part of hardware could be related to that strange behavior - thanks in advance!

[Chronon]

Your player shouldn't care about its orientation in space (ignoring the case of movement while the HD is spinning).  I can imagine that something is physically moving inside of your player and causing a short or breaking a connection.  In this case, I would tend to suspect a cable or wire.  Any loose wires associated with the side buttons, LCD or microphone?  Does it sound like anything is loose inside of your player?

Does the Hold switch have any effect on this behavior? 

[michael]

The problem occurs on a certain attitude in space, always. The only working button then is reset, or to turn the player back into a horizontal "working-position" - hold-switch does´nt have any effect on that. If I turn the player into that attitude very slowly, I can even find the point holding the played audio downpitched before the player would freeze completely - maybe some kind of "flowing" short?
I´ve checked the LCD, mic-wires, buttons and the hold-switch on the pcb - they´re not loose. I did´nt checked underneath the LCD. I don´t want to risk that since the display works well too and it still seems fixed and is firmly sealed by the  plastic foam around it.
The last section I cannot see inside is underneath the daughterboard. But after all trying I do´nt suggest an USB/ATA-issue.
All around with my only eyes and ears I cannot see or hear any moving parts "inside" that could cause this failure. So a physically moving part must be very small or, and thats my actual suggestion, it is a loose part of the player itself, a broken solder connection or such. But how to find?
Any idea what loose part/chip due to the described behavior that could be?